1. Field of the Invention
The present invention relates to a safety steering shaft of a vehicle and specifically relates to a steering shaft deformable in response to a force corresponding to frontal impact of the vehicle for extremely weakening the force.
2. Description of the Prior Art
Two typical types of safety steering shaft for weakening a force correspondng to frontal impact on a vehicle are known. One is a disengagement type coupling which disengages when it receives an excessively large force corresponding to frontal impact of the vehicle. A device of this type is disclosed in Japanese Patent Publication No. SHO 51-102759 and U.S. Pat. No. 3,960,031. The other type of safety steering shaft known heretofore is a device including a deformable member which can deform permanently and weaken a transmitted force by permanent deformation when it receives a force corresponding to frontal impact of the vehicle. A device of this type is disclosed in U.S. Pat. No. 3,457,800. Devices of the latter type are superior to devices of the former type insofar as devices of the latter type can transmit steering force to a car wheel after it has deformed. The present invention relates to a device of the latter type.
In the past, devices of the latter type which include a deformable member have occupied a large space making it difficult to mount the device in a vehicle where space is limited. This is especially true in a vehicle having a front engine front drive system. For example, a steering shaft which includes a deformable bellows portion requires a considerably long bellows portion occupying large space to ensure adequate energy absorption. If the bellows portion is shortened, deformation of the portion becomes difficult and the amount of absorbed energy becomes undesirably small.